The present invention relates to fluid control devices, for example, for use in apparatus for producing semiconductors.
For example, FIG. 6 shows a fluid control device for use in apparatus for producing semiconductors. The device consists of a plurality of lines each comprising a massflow controller 31, two inlet on-off valves 32, 33 provided at the inlet side of the controller 31, and two or three outlet on-off valves 34, 35, 36 arranged at the outlet side of the controller. The inlet on-off valves 32, 33 are used for selectively supplying one of two kinds of gases, i.e., process gas A and purge gas B, while the outlet on-off valves 34, 35, 36 are provided for a line leading to a process chamber, a vent line and an evacuating line for a change-over from one line to another. Process gas A is a gas of which high purity is required and which is expensive. Such a fluid control device has channels for passing the gases A and B, i.e., a main channel 37 in communication with the inlet of a channel within the massflow controller 31, a relatively long subchannel 38 and a relatively short subchannel 39. Conventionally, the relatively short subchannel 39 is thought useful for passing process gas A to be assured of high purity in ensuring the purity of process gas A and reducing the amount thereof to be used.
Our research has revealed that the use of the relatively short subchannel for passing the process gas which should be held at high purity eventually fails to assure the process gas of its purity and to achieve a reduction in the amount of the gas to be used.
An object of the present invention is to provide a fluid control device which is optimized in ensuring the purity of the fluid, such as process gas, to be assured of high purity and in reducing the amount thereof to be used, by introducing the concept of a minimized dead volume (stagnant portion of fluid) in connection with the fluid of which high purity is required.